Morphological and functional indicators were investigated of donor leukocyte concentrates mixed at a ratio of 1 to 1 with three versions of cold-protective and kept at an undercooling temperature (-10 degree C) for 24 hours, and with a cryoprotector of optimal composition for 12 days,. An optimal version of a non-freezing cold-protective solution was found. It was determined that 76+/-4 % of the neutrophils retain there ability of phagocytosis among the viable cells (81+/-5 %) after a 12 day hypobiosis. Thus the results testify to a high morphofunctional safety of human blood leukocytes which experienced cold-hypobiosis (-10 degree C) in an original non-freezing solution not requiring washing after re-warming.